Tiny Bubble?

An Impala, 2008, 3.5L is making creaking and gurgling sounds after a drive. When I shut the car off, the noise begins withing the first 30 seconds to a minute. There are tiny bubbles streaming into the coolant reservoir from the overflow tube. The coolant level is not low. The car does not overheat, There is no evidence of coolant in the crankcase or oil in the cooling system. I should mention that this is intermittent. I suspect it will be more constant as the weather gets warmer. Do I have a head gasket leak, a bad radiator cap, a thermostat problem?

Keep a close eye on coolant level. You might have a head gasket getting ready to go.


You can get a cheap head gasket leak tester that will tell you. It draws air from the radiator through a liquid that changes color if combustion byproducts are in it.

Just make sure you do it right, because if you draw any coolant into the test vessel, the test liquid will also change color and make you think you have a head gasket leak. :wink:

The cooling system cap may not be holding pressure. After turning off the engine squeeze the upper radiator hose, it should be hard like an inflated bicycle tire. If the hose collapses with no resistance the cap is not holding pressure, this causes boiling after shut off.


I considered getting this sort of a device at Harbor Freight. The reservoir is not pressuried; do you think that woujld be enough to sense the presence of combustion gases?

Sometimes, it feels squishy, like there is nothing in it. Thanks.

Yes, it’ll work if you follow the instructions. You do it in the radiator, not the reservoir, and you hook the tester up to engine vacuum which draws air through the tester. It doesn’t require pressurization in the coolant system (which is good, 'cause the radiator cap is off!). Obviously, do not open the radiator cap unless the engine is cold.

Next step, replace the radiator cap.
I would also replace the thermostat at this age.
I would also use only OEM parts, not aftermarket.

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Cleaning the rubber gasket on the cap and the mating surface on the radiator may make a difference. The sealing is a function of that interface, plus the spring tension the cap provides.

I agree to use OEM parts. I wouldn’t disturb the thermostat unless there was evidence of a problem with it.

Good suggestion on cleaning the gasket on the radiator cap. It seems like a good place to start in the process of eliminating possibilities. Thanks.

Never used one of these. Thanks.